Antioxidant and anti-stress properties of postbiotics produced by Lysinibacillus macroides G117

In this study, Lysinibacillus macroides G117 was isolated from vinegar residue, and the probiotic activity of its postbiotics was determined in Artemia salina and Scophthalmus maximus. First, the functional genome of L. macroides G117 was analysed. The total length of the genome was 4,728,501 bp, composed of one ring chromosome and two ring plasmids. Two gene clusters, β-lactone and type III polyketide synthases (T3PKS), well-known for anti-toxic, anti-inflammatory, antioxidant, anticancer activities, were predicted through the antiSMASH database. In addition, probiotic genes for antioxidants, stress resistance, and anaerobic respiration were identified using the KEGG database. These results suggest that L. macroides G117 could be used as a probiotic in aquaculture. To further assess the probiotic properties of L. macroides G117, postbiotics were cultured and collected. Based on the survival rate of pesticide-stimulated A. salina, the optimum culture condition of L. macroides G117 was analysed. The optimal culture conditions were 1% sucrose, 1.5% yeast extract, 0.1% MgSO4·7H2O, 30°C, pH 7.8, bottled fluid volume 100 mL, shaking speed 180 rpm, inoculation quantity 0.5%, and fermentation for 48 h, with a 15% increase in survival rate of A. salina with the addition of optimised postbiotics. Untargeted metabolomic analysis revealed significant differences between the non-optimised and optimised postbiotics, mainly in amino acid and carbohydrate metabolites. Notably, postbiotics significantly increased the antioxidant enzymes in A. salina (catalase (CAT) and total superoxide dismutase (T-SOD)) and S. maximus (T-SOD) and decreased malondialdehyde (MDA) content. In addition, the activities of anaerobic respiratory-related enzymes (lactate dehydrogenase (LDH) and pyruvate kinase (PK)) were significantly increased, whereas those of aerobic respiratory-related enzymes (malate dehydrogenase (MDH)) were significantly decreased in S. maximus. These results suggest that L. macroides G117 postbiotics could improve the antioxidant and anti-stress abilities of the two types of organisms.